1. Field of the Invention
The present invention relates to a rotary cutting tool having a plurality of helical peripheral cutting edges with unequal helix angles formed on a circumferential surface of a tool body.
2. Prior Art
One conventional end mill disclosed in Japanese Patent Publication No. 30-5244 includes a plurality of helical peripheral cutting edges formed on a circumferential surface of a tool body at its forward portion and having helix angles different from one another so that circumferential pitches of the peripheral cutting edges are different from one another in any plane perpendicular to an axis of rotation of the tool body. In such an end mill, the respective cutting edges have been subjected to cutting loads exerted in different directions for different time intervals. Accordingly, the end mill is not susceptible to a vibration having such a frequency that the end mill is resonated with the machine tool, and therefore the end mill is prevented from being subjected to chattering, resulting in an improvement of the cutting performance.
The end mill, however, has a drawback of taking much time and skill for its manufacture. In addition, its cutting performance has not been sufficient mainly because chips produced during cutting operation are not removed smoothly.